This invention relates generally to the dimple configuration on the surface of a golf ball and more particularly to an elongated dimple configuration and the method of obtaining that configuration.
Golf balls are now being produced having various dimple patterns, dimple sizes, and geometric dimple patterns. Generally speaking, all of these dimples are configured so as to have a substantially constant geometric surface. Whether circular or multi-sided, the dimples are designed so that the geometrical configuration of each dimple is substantially the same regardless of its size. In this type of dimple arrangement, the dimples are normally configured in some pattern such as an octahedron, dodecahedron, or the like, or are configured so as to provide sections within the hemisphere, whether those sections number four, or six, or whatever desired configuration. Normally, the dimples are arranged in a desired pattern within each section and then this pattern is repeated for each section. The standard procedure is that each hemisphere has the same number of dimples and in substantially the same pattern and the hemispheres may be rotated with respect to each other depending upon the position of the mold halves.
U.S. Pat. No. 5,356,150 issued Oct. 18, 1994 and assigned to the assignee of the present invention discloses a golf ball having a plurality of dimples formed on the spherical surface of the golf ball, with the surface defining opposite poles and an equator midway between the poles so as to divide the surface into two hemispheres. The hemispheres have substantially the same dimple pattern and each dimple pattern comprises a dimple-free area surrounding the pole, a dimple-free area adjacent the equator, and a plurality of substantially identical sections extending between the pole and the equator, with each of said sections having a dimple pattern which comprises a plurality of elongated dimples. The axis of each dimple may extend in a direction between a line parallel with the equator and a line between the equator and the pole. The majority of the dimples overlap at least one adjacent dimple. The method used for obtaining this pattern is to locate a plurality of substantially similar geometric dimples on each of the hemispheres and move the outline of the dimples tangentially along the surface of the ball in the selected direction until it passes beyond the spherical surface so as to form elongated dimples in the surface of the ball.
The present invention is an improvement over the ball disclosed in U.S. Pat. No. 5,356,150 in that it improves the aerodynamics of that ball. It has been found that the use of a dimpled surface where substantially all of the dimples overlap does not necessarily have the optimum aerodynamic characteristics during the flight of the ball. The present invention may be formed by the basic movement as set forth in the above-described patent and uses at least two different sizes of elongated dimples with substantially no dimple overlap. In order to obtain substantially maximum dimple coverage of the surface of the ball a first set of dimples are provided which are formed by extending the dimple depression in a selected direction which may extend until it terminates as it leaves the surface of the ball. For the purposes of clarification, this movement will be referred to as full dimple drag. A second set of dimples are provided by using a dimple drag less than the full distance described above which will be referred to as partial dimple drag. This second set of elongated dimples permit the use of shorter elongated dimples which provides a substantial dimple coverage with substantially no dimple overlap. Additional elongated dimples may be added using dimple depressions of differing diameters and depths. Further, a pattern may include dimples having different partial drag lengths.
According to another object of the invention, elongated dimples may be formed by drilling into a spherical surface to a first depth with a drill bit having a first radius and by displacing the drill bit and/or the spherical surface in a first direction during the drilling step. The first direction may be either straight (i.e. linear or monotonical) or curved. In addition the drill bit and/or the spherical surface may be further displaced in a second direction during the drilling step to form an elongated dimple with two axes.